Optical recording media such as the Blu-ray Disc (registered trademark) are known. In the optical recording media, recording and reproduction of information by use of a semiconductor laser are performed.
The recording to an optical disk by use of a semiconductor laser is greatly affected by variation in the laser power attributed to the temperature and change over time, various kinds of skews and offsets attributed to an adjustment error at the time of the manufacturing, and a recording condition gap in the drive control. Therefore, particularly for recordable optical disks such as a write-once disk and a rewritable disk, variation in the laser drive circuit and the optical element is suppressed and precise light-emission waveform control is carried out.
In an actual information recording device, in general, immediately before data recording, the optimum laser power is sought and the recording laser power and strategy are adjusted to optimize the recording condition by using the test write area (optimum power control (OPC) area) disposed in each recording layer.
In the trial writing process (test write) for this recording laser power adjustment, removal of the above-described perturbations, optimization of the recording power, and optimization of the laser drive pulse need to be carried out in the state in which the optimum recording condition is unclear.
In the seeking of the optimum condition, the test write area is irradiated with laser light having excessively-high energy and the laser irradiation is performed with an improper width of the laser drive pulse (laser emission time) depending on the case. Thus, serious damage is possibly given to the test writing area in the recording layer.
Furthermore, in a so-called multi-layer optical disk, in which plural recording layers are formed over a disk substrate, recording/reproduction of a certain recording layer is affected by another recording layer.
For example, change in the transmittance of a recording layer attributed to recording occurs, which possibly precludes light irradiation of the intended recording layer with a proper amount of light.
Moreover, the transmittance change has a dependency on the recording power. Therefore, the transmittance change, i.e. the degree of the influence on the other recording layers, cannot be controlled in a place where recording is performed with variation in the recording power like the OPC area.
These facts lead to a problem that the desired OPC control cannot be realized and derivation of the accurate optimization condition is difficult depending on the recording statuses of the other recording layers.
Specifically, in the case of performing trial writing in the OPC area in a certain recording layer and adjusting the laser power, this trial writing is affected by the test write area that is in another recording layer and disposed at the same position in the planar direction (disk radial direction) as that of this OPC area (i.e. such a position as to overlap with this OPC area in the thickness direction (=layer direction)).
To address this problem, as the related arts, there have been devised a method in which the test writing areas in different recording layers are mutually shifted along the radial direction of the recording layer and a method in which the same radial position is not used for trial writing between the trial writing areas in different recording layers, as is seen in Patent Document 1 shown above, for example.
Also in the double-layer standard of the existing Blu-ray Disc, it is prescribed that the test writing areas of the respective recording layers, disposed in the lead-in zone on the disk inner circumference side, are so disposed as to be shifted from each other along the radial direction of the recording layer.
Prior Art Documents
Patent Document
Patent Document 1: PCT Patent Publication No. WO05/034110 brochure
Patent Document 2: Japanese Patent Laid-open No. 2004-295940